Trimethylsilane enol

A solution of the trimethylsilyl enol ether of propionyl trimethylsilane (5 mmol) (Chapter 12) and benzaldehyde diethyl acetal (5 mmol) in dichloromethane (10ml) was added to a solution of BF3.OEt2 (5 mmol) in dichloromethane (5ml), cooled to —78 C. After being stirred for lh at -78°C and 2h at -30°C, the mixture was quenched with excess saturated sodium hydrogen carbonate solution, and extracted with ether. Concentration and distillation gave the product -ethoxy acylsilane, (4.6mmol, 95%). b.p. 105-106 C/2mmHg. Treatment of this alkoxy... 

Silyl enol ethers.1 Aldehydes, ketones, ot,p-enals, and a,p-enones are converted into the silyl enol ethers in moderate to high yield by reaction with iodo-trimethylsilane, generated in situ, and N(C2H5)3 at 25° in acetonitrile. In some cases intermediate stable 1,2- or 1,4- adducts can be isolated. Thus the 1,2-adduct a hag been isolated as an intermediate in the reaction of some aldehydes and shown to decompose to the silyl enol ether. 

Mukiayama aldol reactions between silyl enol ethers and various carbonyl containing compounds is yet another reaction whose stereochemical outcome can be influenced by the presence of bis(oxazoline)-metal complexes. Evans has carried out a great deal of the work in this area. In 1996, Evans and coworkers reported the copper(II)- and zinc(II)-py-box (la-c) catalyzed aldol condensation between benzyloxyacetaldehyde 146 and the trimethylsilyl enol ether [(l-ferf-butylthio)vinyl]oxy trimethylsilane I47. b82,85 Complete conversion to aldol adduct 148 was achieved with enantiomeric excesses up to 96% [using copper(II) triflate]. The use of zinc as the coordination metal led to consistently lower selectivities and longer reaction times, as shown in Table 9.25 (Eig. 9.46). 

Recently, analogues of nucleosides [60], natural products Huperzine-A [61] and Hydroartemisinin [62], and inhibitors of metallo-/ -lactamases have been synthesised [63]. With acylsilane electrophiles, the initial adducts undergo Brook rearrangement which is interrupted by -Si bond fission with loss of fluoride anion (Eq. 16), leading to the formation of extremely useful difluoro-enol silanes [64]. Of the various fluoride sources employed, the tetrabutylam-monium triphenyldifluorostannate described by Gingras appears to be particularly effective. The numerous other methods for trifluoromethylation formed the subject of an exhaustive review [65]. More recently, the Olah group described a chlorodifluoromethyl trimethylsilane which is expected to have a rich chemistry [66]. 

Co2(CO)8-catalyzed reactions of benzylic acetates with trimethylsilane and CO proceed under mild reaction conditions to give trimethylsilylethers of /3-phenethylalcohol in 43-76% yield. The highest yields are observed for benzyl acetates with electron-donating substituents.111 Secondary alkyl acetates are also good substrates in the reaction system, yielding enol silyl ethers.112 In addition, the cobalt complex is an effective catalyst for siloxymethylation of five-membered cyclic ortho esters, as shown in Eq. (41).113... 

Carbonyl Addition Diethylzinc has been added to benzaldehyde at room temperature in the presence of an ephedra-derived chiral quat (8) to give optically active secondary alcohols, a case in which the chiral catalyst affords a much higher enantioselectivity in the solid state than in solution (47 to 48, Scheme 10.6) [30]. Asymmetric trifluoromethylation of aldehydes and ketones (49 to 50, Scheme 10.6 [31]) is accomplished with trifluoromethyl-trimethylsilane, catalyzed by a quaternary ammonium fluoride (3d). Catalyst 3d was first used by the Shioiri group for catalytic asymmetric aldol reactions from silyl enol ethers 51 or 54 (Scheme 10.6) [32]. Various other 1,2-carbonyl additions [33] and aldol reactions [34] have been reported. 

Photochemically-induced addition of bromotrichloromethane to 1-ethoxy-1-trimethyl-silylethene, the ethyl enol ether of acetyl trimethylsilane, generates a 1 1 adduct which provides 3,3-dichloropropenoyl trimethylsilane (20) on solvolysis. Treatment of this material with lithium alkyl cyanocuprates resulted in addition-elimination to give the -isomers of the 3-substituted a,/J-unsaturated acyl silane products (Scheme 50)135. 

In an interesting transformation, reaction of benzoyl trimethylsilane with lithium enolates derived from various methyl ketones gives rise to 1,2-cyclopropanediols, predominantly with the cis configuration, in good yields (Scheme 77). The reaction, which proceeds through addition, Brook rearrangement and cyclization, is also successful with a,/l-unsaturated acyl silanes vide infra, Section IV.D)187. 

Dichloropropenoyl trimethylsilane, prepared by photochemically induced addition of bromotrichloromethane to the ethyl enol ether of acetyl trimethylsilane, undergoes completely regioselective addition-elimination upon treatment with lithium cyanocuprate reagents, giving the Z -3-chloroalk-2-enoyl silane products (vide supra, Section III.D.3)135. 

Phenylthiotrimethylsilane adds to propenoyl trimethylsilane under the influence of Lewis acid to give l,3-bis(phenylthio)-l-trimethylsilylprop-l-ene (18). This enol thioether may be deprotonated with f-butyl lithium and alkylated with any of a large range of electrophiles. Subsequent hydrolysis-elimination with mercuric chloride in aqueous acetonitrile provides -substituted a,/J-unsaturated acyl silanes (vide supra, Section III.D.3)132. It should be noted that, in this transformation, the /1-substituent has... 

The selective C-silylation of some zinc enolates on treatment with chloro-trimethylsilane deserves mentioning because it is in clear contrast to the preponderant O-alkylation of other metal enolate reagents. Although this transformation is essentially confined to alkyl bromozincacetate and halozinc-... 

Whereas methyl 2-siloxycyclopropanecarboxylates are thermally stable up to temperatures as high as 170 °C, they readily rearrange at low temperatures under the influence of appropriate Lewis acids. Catalytic amounts (0.05-0.4 equiv.) of iodo-trimethylsilane within minutes to days promote a quantitative ring opening of cyclopropanes 755 to the corresponding silyl enol ethers 156 (Eq. 68, Table 4)88). 

Hosomi, A., lijima, S., and Sakurai, H., A novel aminomethylation of silyl enol ethers with aminomethyl ethers catalyzed by iodo-trimethylsilane or uimethylsilyl trifluorome-thane sulfonate. Tetrahedron I tt.. 23, 547, 1982. 

Diketones can be converted to a-keto enol ethers by treatment with an alkoxy-trimethylsilane (ROSiMea). ... 

When a silyl enol ether is the trimethylsilyl derivative (Me3Si-0-C=C), treatment with methyllithium will regenerate the hthium enolate anion and the volatile trimethylsilane (Me3SiH). The enolate anion can be used in the usual reactions. In a similar reaction, a trimethylsilyl enol ether was treated with Cp2Zr (from Cp2ZrCl2/2 BuLiArHE/-78°C), and subsequent quenching with D2O led to incorporation of deuterium at the vinyl carbon (C=C-D). ... 

Lithiated [bis(phenylsulfanyl)methyl]trimethylsilane reacts readily with a,) -unsaturated ketones to give the enolates 1. Ring closure accompanied by elimination of lithium ben-zenethiolate occurs upon warming in the presence of equimolar amounts of copper triflate to give the 1-phenylsulfanyl-1-trimethylsilylcyclopropanes 2. 

S )-Dibenzyl l-(l-Oxo-l,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-l,2-dicarboxylate (Catalyzed Asymmetric Amination of a Ketone Silyl Enol Ether with an Azo Ester).244 A solution of silver perchlorate (0.040 mmol) and (R)-BINAP (0.048 mmol, 12 mol%) in THF (1 mL) was stirred at room temperature for 30 minutes, cooled to —45°, and treated with dibenzyl azodicarboxylate (0.44 mmol). After stirring for 10 minutes, (3,4-dihydronaphthalen-l-yloxy)trimethylsilane (0.4 mmol) in THF (0.5 mL) was added and the mixture was stirred at —45° for 5 hours. Aqueous HF (20%) and THF (1 1) were added and the mixture was stirred at room temperature for one hour after which time it was made basic with aqueous NaHCC>3 solution and extracted with CH2CI2. 

Reaction of lithium enolates from primary alkyl esters with chloro-trimethylsilane occurs under mild conditions and affords the water-sensitive ketene-acetals RCH=C(OR )(OSiMe3). f-Butyl esters yield comparable amounts of the O and C-silylated derivatives [5],... 

Trialkylsilyl halides show a great propensity to react with the oxygen rather than the carbon of enolate anions. Stork showed that 0-alkylation allows enolates to be trapped as the trialkylsilyl enol ether, which is most useful for kinetic enolates in which a lithium enolate (such as the kinetic enolate derived from 2-methyl-cyclohexanone and LDA) is reacted with trimethylsilyl chloride to give an isolable intermediate, 112. jjig enolate is trapped with high efficiency, and conversion to the enolate is readily accomplished by treatment with methyllithium, which generates the kinetic enolate (113) and the volatile trimethylsilane (Me3SiH). This... 

Araki Y, Kobayashi N, Ishido Y, Nagasawa J (1987) Synthetic studies with fluorinated intermediates. 3. Highly stereoselective C-a-D-ribofuranosylation. Reactions of ribofuranosyl fluoride derivatives with enol trimethylsilyl ethers and with allyl trimethylsilane. CarbohydrRes 171 125-139... 

The reaction shown in equation 170 is, however, the only known example where a silene reacts with its acylpolysilane precursor. Whereas sUenes of the type (Me3Si)2Si=C(OSiMe3)R do not react with their polysUane precursors, they readily react with less sterically congested acylsilanes. Thus, mesitylsilene 349 gives with benzoyl trimethylsilane a mixture of the diastereomeric sUoxetanes /Z-511 in 95% yield (equation 171). Typically, the adamantylsilene 150 gives with benzoyl trimethylsilane the nominal [4 + 2] cycloadduct 512 in 89% yield (equation 172). The silyl enol ether 513 is the result of an ene -type reaction which occnrs between 150 and acetyl triphenylsilane, a carbonyl compound having an activated hydrogen (eqnation 173). ... 

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